Replaceable tip shear proof punch

ABSTRACT

A shear proof punch with heel aligning structure formed as a part of the punch tip retainer but without difficult machining tolerances.

United States Patent H Patterson Sept. 18, 1973 REPLACEABLE TIP SHEARPROOF PUNCH [75] Inventor: Clinton E. Patterson, Minneapolis, [56]Reierences cued Minn. UNITED STATES PATENTS 3,348,443 l0/l967 Smith etal 83/635 X [73] Ass'gnee r t 3,296,905 1/1967 Killaly 83/635 x Filedi P1972 Primary Examiner.|. M. Meister N Attorney-L. A. MaCeachl'On [57]ABSTRACT [52] U.S. Cl 83/637, 88330663958, 8834/6536, A Shear proofpunch with heel g g Structure [51] Int Cl 1/12 formed as a part of thepunch tip retainer but without 58 Field of Search 83/635, 637, 684-690,machmmg mle'ances' 7 Claims, 7 Drawing Figures REPLACEABLE TIP SHEARPROOF PUNCH BACKGROUND OF THE INVENTION This invention relates to a formof cutting die and punch arrangement in which the punch has elementsthat prevent it from becoming misaligned with the die when only aportion of the punch is actually cutting. This form of punch has becomeknown in the trade as a shear proof punch. The elements that keep thepunch aligned with the die are known as heels. They are members that arespring loaded to extend below the surface of the punch when it is notcutting and which are forced to retract until their lower surface formsa portion of the cutting punch only if there is material to be cut intheir path. When no material forces the heel to retract, it precedes thebalance of the punch tip into the die to assure that the punch will notmove laterally as a result of cutting with a portion only of the punchsurface. As an economy of language, these punches will be referred tohereafter as shear proofs.

One of the principal drawbacks to the shear proof from the point of viewof the user is the rather high expense of punch when made in theconventional manner. One of the more satisfactory methods of making theheels is to make them of rod stock and then cut away whatever portion ofthe heel as round that does not conform to the shape of the punch forwhich it will serve as a heel. As a result, the portion of the heel thatfunctions as part of the punch for cutting is asymmetrical. It must beheld in an aligned position, therefore, when cutting as part of thepunch or when serving as a lateral movement restrainer either one. Mostof these heels are currently held in an aligned position by means ofsmall plates that are accurately made and fitted to the side of thepunch tip. The plates are held there with cap screws which the mostcareful makers secure with safety wire. No other means of securing thecap screws seems to assure that the screws will not loosen as a resultof running the punch in a press. The complexity of this conventionalstructure causes the manufacture and assembly of the parts for theseshear proofs very time consuming which is to say expensive.

In a manner of speaking, the conventional shear proof is a replaceabletip unit. In fact, however, there is no little value in the retainer ofconventional structure, it does not pay to have that part returned to beused again. This invention addresses itself to the solution of both ofthe problems described above by making a shear proof with a replaceabletip in which the retainer carries the heel aligning structure.

BRIEF DESCRIPTION OF THE INVENTION There are two main features that areparticularly important. The first of these is the concept of having theheel aligning structure part of the retainer rather than having itsecured directly to the punch tip. The second point is having thereference surface of the retainer, against which the punch and heelsbear when they are cutting, spaced vertically from the heels aligningsurfaces to reduce the criticality of the machining necessary to make auseable punch. If the heel aligning structure were so near to thereference surface as to have portions of the aligning structure in thesame plane as the reference surface or nearly so, those surfaces wouldhave to be at nearly exact right angles to each other for the punch tofunction well.

The punch tip retainer of this invention is longer than conventionalretainers and has fingers which extend down along the sides of the tip.At the ends of these fingers are what are called herein pads. The padsare rather narrow and no portion of them is anywhere near the referencesurface horizontal plane. The reference surface of the punch tipretainer against which the punch tip rests to provide the support forthe tip to be forced to shear the material being cut by the punch is ata different elevation than any part of the pad on the heel aligningfinger. These facts make the machining of the retainer substantiallyless demanding than it otherwise would be. Thus without generating anearly impossible machining job, a shear proof is provided in which theheel aligning structure is on the retainer rather than the punch tip.

To assure that the heel aligning structure is in initimate contact withthe sides of the punch tip and hence will assure good aligning, thespace defined by the pads of the fingers is never larger than thedimensions of the punch tip. It may be smaller to assure close contactbetween the sides of the punch tip and the finger pads. For this reasonthe retainer is made from spring steel so that the fingers can yield ifneed be to accept the tip. Such a fit is assured by giving a nominaldimension to both the tip and the retainer opening that is the same andproviding only a minus tolerance for the opening in the retainer andonly a plus tolerance for the punch tip. If the tip and the retaineropening were by some chance to exactly match the nominal size, theywould fit precisely. Since mostmachining tolerances are a recognition ofthe impracticality of getting exact dimensions in an economically soundperiod of time, the tip is almost invariably slightly larger than theopening. The most satisfactory spring steel known presently is calledAISI Standard 8-7. I

In at least one form of the device disclosed here, the tip can beremoved and replaced in the retainer without removing the retainer fromthe punch holder of the press.

All of this structure will be described in detail in connection withaccompanying drawings which are briefly described as follows:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a fragmentary side elevationof the invention, a portion of a press and a die;

FIG. 2 is an exploded side elevation of the invention drawn to a smallerscale than the one used in FIG. 1; broken lines shown hidden parts andthe alignment of parts;

. FIG. 3 is a bottom view of the punch tip retainer shown in FlG.-l andat the same scale as that figure; broken lines show hidden parts;

FIG. 4 is a vertical section of the retainer shown in FIG. 3 and takenon the line and in the direction of the arrows 4--4; it is drawn to thescale of FIG. 1;

FIG. 5 is a perspective view of the punch tip of figures I and 2 and isshown in a scale that is between those used in those two figures;

FIG. 6 is a perspective view of an alternate form of of the structureshown in FIG. 5 and drawn to the scale of FIG. I; and

FIG. 7 is a vertical section of the punch tip of FIG. 6 and taken on theline and in the direction of the arrows 7-7 in FIG. 6; the tip is shownsecured to a retainer and holder that are also shown in section anddrawn to the scale of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1, is a punch holder thatis part of the turret press with which the shear proof punch is used andto which the punch retainer 11 is conventionally secured by a cap screwrepresented by the broken lines 12. The punch tip is designated 14 andis secured to the retainer by cap screws one of which is represented at15. There are .four heels, one for each side of the square. Three ofthese can be seen at 16, 17 and 18. The die is numbered 19 and a sheetmaterial being cut is 20. As is clearly seen in FIG. 1, the sheetmaterial has been cut once and has an opening 21. This opening ismisaligned with the opening 22 of the die 19 so that only heel 16 isacting as part of the cutting punch on this stroke. The heels l7 and 18are seen to be below the surface of the die 19 and into the opening 22in the die 19. Heel 16 is partially retracted as a result of engagingmaterial 20. Spring 24 which urges heel l6 downward is partlycompressed. Because the heel 17 has encountered no resistance, spring 25is urging heel l7 outward as far as the structure of the tip will allow.Punch tip 14 has not yet engaged the sheet of material 20 as shown inFIG. 1, hence the heels l7 and 18, as well as the heel that is directlyacross from heel l7 and obscured by heel 17, will be well into theopening 22 of die 19 before the cutting pressure is applied to tip 14.

In FIG. 2, cap screws and 26 fit into the wells 27 and 28 of retainer 11and engage threads in tip 14 to hold those two parts together. Heels 16,17 and 18 and their respective springs 24, 25 and 29 fit into wells (notshown in FIG. 2) in retainer 11 and engage the heads 16a, 17a and 18a ofthe heels 16, 17 and 18. The springs urge the heels outward as far asthe enlarged portion 30 of heel groove 31 for heel 17, for example, willpermit. In'FIG. 5, the balance of the heel groove enlargements may beseen at 32, 34 and 35. In addition to heel groove 31 for heel 17 may beseen heel groove 36 for heel. 18. The two wells 37 and 38 are threadedand receive the cap screws 15 and 26.

Referring now to FIG. 3, retainer 11 has the opening 29 to receive thepunch tip 14. It is slightly larger than the punch tip so there is aslight clearance between them. The fingers 41, 42, 44 and 45 are one thefour sides of the opening and engage the four sides of the tip 14 whenit is engaged in opening 39. Well 46 is threaded to receive the capscrew 12. Indexing notches 47 and 48are conventional and have no specialsignificance relative to this invention. The wells 49, 50, 51 and 52receive the four springs for the heels.

In FIG. 4, the fingers 42 and 41 are shown clearly to have the pads 54and 55 respectively which extend inward from the balance of the fingers.These pads are ground or otherwise machined to be the surfaces whichwill hold the heels aligned with the punch tip. The bottom 56 of well 39is a reference surface against which the end 57 of punch tip 14 rests.It will be noted that no portion of pads 54 and 55 are anywhere near thesurface 56 with reference to their vertical positions. For this reason,surface 56 does not have to be pre-' cisely at right angles to thevertical surfaces of the pads as would be the case if the fingers didnot have pads and spring fingers. If there were unyielding punch tipcontacting and heel aligning members right next to the referencesurface, the precision of workmanship that would be required would beextreme.

In FIG. 6 a form of punch tip is shown that varies from that shown anddescribed previously in only one main respect. In FIG. 6 it can be seenthat there is an unthreaded well 65 in place of the two threaded wells37 and 38 in FIG. 5.

Turning now to FIG. 7, the use of this central well 65 to receive thecap screw 60 which is reached and turned from the cutting end of thetool punch rather than the via the rear of the retainer as in the formof the invention shown in FIGS. l-5. In FIGS. 6 and 7 all parts.

that are the same in form and function to counterparts in the form ofthe invention shown in FIGS. 1-5 are given the same number designationsfollowed by letter suffixes. Parts that are different in the form 'ofthe invention illustrated in FIGS. 6 and 7 are given new numbers. InFIG. 6 for example, only the center well 65 is different. All of theother portions of the tip 14a from 300 to 57a are appropriatelydescribed by reference to the descriptions of parts '30, 31 etc.

As is clearly shown in FIG. 7, the retainer 11a is held in the punchholder 10a by the cap screw 12a. Cap screw 60 in well 65 uses the lowerend of this threaded well 46a to hold the tip 14a in the retainer 11a.

Cap screw 60 has a groove 61 formed in it into which the snap ring 62fits. Snap ring 62 is no thicker than the very shallow well 64 is deep.The cap screw 60 can turn in relation to the snap ring 62, but there isno axial movement between them or more accurately very little axialmovement. All the rest of the parts are essentially the same as theirsimilarly designated counterparts. Because the heels 16 and 18 havetheir heads designated as and respectively, the heels in this figure arecalled 16b and 18b and theirheads 16c and 180.

OPERATION This portion of the application deals with replacing the tips;the punch is used in slotting the same as a conventional punch is used.

Replacement of the tip 14 in the structure shown in FIGS. l-5 isaccomplished by removing the punch holder 10 from the press andseparating the assembled retainer and tip from the holder by unscrewingcap screw 12. Cap screws 15 and 26 are then accessible and can beremoved. It may be necessary to use a mechanical assist to remove tip 14from the retainer 11. Well 46 will give access to the back of the punchtip so that an arbor press or some other formof mechanical aid can beused to puch the tip free. A new tip can then be pressed into theretainer 1 l. Screws 15 and 26 are then used to secure the two togetherand it may then be reassembled to the punch holder.

When the form of the invention shown in FIGS. 6 and 7. is used, thereplacement job is still easier. Once the punch holder 10a is removedfrom the press, it can be turned so the tip 14a is facing up. Access tothe cap 60 is immediate'down well 65. Furthermore, as the cap screw isbacked out of well 460, snap ring 62 pushes on surface 57a of tip 14aand serves asa built in screw jack to push the tip 140 out of retainer11a. Cap screw 60 has less length of threads than the distance from thefinger pad 54a to the surface 56a of the retainer. Since the sides ofwell 39a clear the tip 144, only the pads serve to position the tip inthe retainer. For this reason, tip 14a can be relieved starting a shortdistance from pad 54:: toward surface 570. Once tip 14a has been movedto the area of relief, the tension applied by the fingers is greatlyreduced or relieved altogether. Tip 140 can be removed with relativeease. Similarly a replacement tip can be removed into retainer 11arather easily far enough to let cap screw 60 engage the threads of well460 before the need of a mechanical assist is felt. The cap screw 60 isthen engaged and is used to move the tip into the retainer for thatportion of the movement during which the friction applied by the springfingers is severe. The cap screw then with the snap ring serves both asa screw threaded means for aiding in the disassembly and reassembly ofthe punch.

This completes the disclosure of the invention, and it is now claimedbelow as required by law.

I claim: 1. A shearproof punch structure including: A. a retainerportion adapted to be secured to a punch holder during use, B. a tipsecured to the retainer in a manner allowing them to be separated whendesired, C. heels secured to said tip for limited sliding movementrelative thereto, D. means for urging said heels to one limit ofmovement, and E. heel aligning structure secured to said retainer. 2.The shear proof punch structure of claim 1 in which the heel aligningstructure is spring fingers hav- 6 ing pads.

3. The shear proof punch structure of claim I in which the tip isreleaseably secured to the retainer by means actuated at the cuttingface of the punch tip.

4. The shear proof punch structure of claim 1 in which the heel aligningstructure is spring fingers and the means for securing the heel and tiptogether is screw thread means that also can force the tip and retainerapart and draw them together.

5. The shear proof punch structure of claim 1 in which said retainer hasa reference surface against which the tip bears when in operablecondition and characterized by having the reference surface spaced fromthe heel aligning structure vertically.

6. The sheer proof punch structure of claim 5 in which the heel aligningstructure is spring fingers having pads and the distance between pads isnever greater than the corresponding distance between faces of the tipthat the pads will engage.

7. The sheer proof punch structure of claim 6 in which the tip andretainer are releaseably secured to each other by a cap screw having agroove in it, and a snap ring in said groove that engages said tip whensaid cap screw is backed off to push said tip from said retainer; saidcap screw head being accessible at the cutting face of said tip.

1. A shearproof punch structure including: A. a retainer portion adaptedto be secured to a punch holder during use, B. a tip secured to theretainer in a manner allowing them to be separated when desired, C.heels secured to said tip for limited sliding movement relative thereto,D. means for urging said heels to one limit of movement, and E. heelaligning structure secured to said retainer.
 2. The shear proof punchstructure of claim 1 in which the heel aligning structure is springfingers having pads.
 3. The shear proof punch structure of claim 1 inwhich the tip is releaseably secured to the retainer by means actuatedat the cutting face of the punch tip.
 4. The shear proof punch structureof claim 1 in which the heel aligning structure is spring fingers andthe means for securing the heel and tip together is screw thread meansthat also can force the tip and retainer apart and draw them together.5. The shear proof punch structure of claim 1 in which said retainer hasa reference surface against which the tip bears when in operablecondition and characterized by having the reference surface spaced fromthe heel aligning structure vertically.
 6. The sheer proof punchstructure of claim 5 in which the heel aligning structure is springfingers having pads and the distance between pads is never greater thanthe corresponding distance between faces of the tip that the pads willengage.
 7. The sheer proof punch structure of claim 6 in which the tipand retainer are releaseably secured to each other by a cap screw havinga groove in it, and a snap ring in said groove that engages said tipwhen said cap screw is backed off to push said tip from said retainer;said cap screw head being accessible at the cutting face of said tip.